1. Field of the Invention
The present invention relates to a mobile communication system, a method of controlling operation thereof and a node used in the system, and more particularly, to a configuration system of a signalling connection on an interface between a Core Network and a Radio Network Controller (RNC), the signalling connection being necessary when providing a broadcast or multicast service supporting high-speed data communication called MBMS (Multimedia Broadcast Multicast Service) in the mobile communication system.
2. Description of the Prior Art
Techniques of configuring a signalling connection operable for transfer control of various control signals in a W-CDMA (Wideband-CDMA) mobile communication system are defined in “RRC Services provided to upper layers” in Chap. 5 of the specification TS 25.331 (Non-Patent Document 1) prepared by the 3GPP (Third Generation Partnership Project). By referring to FIG. 7, the signalling connection configuring techniques will be described.
It will be observed from FIG. 7 that the W-CDMA mobile communication system comprises a Core Network (CN) 10 including a switching network, a Radio Network Controller (RNC) 22, and a mobile terminal (UE) 51. Between the Core Network 10 and the Radio Network Controller 22, logical connections 111 and 121 are set for transfer of signalling messages, where the logical connection 111 is referred to as a CS Iu connection which is established between an MSC (Mobile-services Switching Center) 11 configuring the Core Network 10 and the Radio Network Controller 22, and is functional for a CS domain corresponding to a CS network having a circuit switching function for voice communication.
The logical connection 121 is referred to as a PS Iu connection which is established between an SGSN (Serving GPRS (Global Packet Radio Service) Support Node) 12 configuring the Core Network 10 and the Radio Network Controller 22, and is functional for a PS domain corresponding to a PS network having a packet switching function. The Radio Network Controller 22 manages radio resources, controls a Node B (radio base station) which is not shown, and the like, and is typified by a handover controlling device.
Established between the Radio Network Controller 22 and the mobile terminal 51 is an RRC (Radio Resource Connection) connection 211 for signalling transfer. The RRC connection 211 corresponds to an RRC signalling connection 711 in the mobile terminal 51. This RRC signalling connection 711 is configured with a CS signalling connection 511 for a CS domain 611 and a PS signalling connection 512 for a PS domain 612.
Thus, the W-CDMA mobile communication system makes it possible to establish in the mobile terminal 51 the signalling connections 511 and 512 corresponding to the CS domain 611 and the PS domain 612, respectively, which is defined in the Non-Patent Document 1.
The W-CDMA mobile communication system having such a configuration may sometimes support a new service such as MBMS (Multimedia Broadcast Multicast Service). More specifically, when a broadcast or multicast service called MBMS supporting high speed, large capacity data communication of moving images or images with sound information is provided, the W-CDMA mobile communication system takes a configuration shown in FIG. 8. FIG. 8 represents the case where the multicast service is provided.
In FIG. 8, the same reference numerals are allocated to the same components as those in FIG. 7. Referring to FIG. 8, there is shown a RAN (Radio Access Network) 21 provided between the Core Network 10 and the mobile terminals 51 to 53, which comprises the Radio Network Controller (RNC) 22 and a Node B 23. Note here that in FIG. 7 only the Radio Network Controller 22 is shown while the Node B 23 is omitted.
Within an MBMS coverage 41 where MBMS multicast service information is distributed, MBMS service subscribing mobile terminals 51 and 52 and a non-subscribing mobile terminal 53 are being present. Multicast is a service for distributing the same data to multiple specified destination addresses (mobile terminals).
In this case, the logical connections for signalling transfer between the Core Network 10 and the Radio Network Controller 22 are set as shown in FIG. 9. As seen from FIG. 9, when the CS signalling connection 511 of the CS domain 611 and the PS signalling connection 512 of the PS domain 612 are established in the mobile terminal 51, and when the mobile terminal 51 further attempts to receive the MBMS service in the current state, there is no need to execute another signalling connection establishment processing for the MBMS service to the mobile terminal 51. More specifically, since the MBMS service is provided in packet communication, an MBMS signalling connection may be regarded as being included in the PS domain having the packet switching function, whereby the mobile terminal 51 is able to use the PS Iu connection 121 which is an already established logical connection.
Thus, when the Iu connection for the PS domain has been established in the mobile terminal, the SGSN 12 does not execute paging processing in conformity with an RANAP (Radio Access Network Application Part) protocol (processing for recognizing one of a plurality of Radio Network Controller areas (cells) that a mobile terminal belongs to).
To the contrary, another mobile terminal 52, in which the signalling connection of the PS domain is not established, requires a new MBMS signalling connection 523 in order to receive the MBMS service and accordingly the SGSN 12 is requested to execute the paging processing. Reference numeral 613 denotes a PS domain of the mobile terminal 52, and 712 denotes an RRC signalling connection of the mobile terminal 52. Reference numeral 212 denotes an RRC connection between the mobile terminal 52 and the Radio Network Controller 22, and 122 denotes an MBMS Iu connection between the Core Network 10 and the Radio Network Controller 22.
As described by referring FIG. 9, if the PS signalling connection 512 for the PS domain is established in the mobile terminal 51 and further the logical connection of PS Iu connection 121 is established between the Core Network 10 and the Radio Network Controller 22 when the W-CDMA mobile communication system attempts to newly support the MBMS service, MBMS signalling may be performed using this PS Iu connection 121.
The signalling connection thus described is, however, shared with both the PS service including an existing packet switched service and such a new MBMS service, which raises the problem such that processing contention is caused between different types of services. More specifically, when an establishment request of a usual packet service (such as a receipt of packet data) is generated while the MBMS service is being provided, the paging processing is not executed because the PS signalling connection has already been established, but the signalling connection that is in use for the MBMS service works also for processing to establish an RAB (Radio Access Bearer) of the packet service. This is more likely to cause the processing contention between the MBMS service and the packet communication service.
Also, another problem may arise in that the processing in the SGSN 12 of the Core Network 10 increases in complexity. More specifically, if the mobile terminal has the established PS signalling connection for usual packet service, a message is transmitted/received using this existing PS signalling connection because of the mobile terminal being designed to have only one signalling connection in the PS domain. Therefore, a new PS signalling connection for the MBMS service does not need to be established. However, the mobile terminal not having the established PS signalling connection needs a new PS signalling connection to receive the MBMS service by which MBMS messages may be transmitted/received. This requires the SGSN to check into PS signalling establishment statuses of each mobile terminal and to determine the signalling connection used for message transmission and reception. Besides, even when the MBMS service is terminated, the SGSN needs to determine whether the mobile terminal is still receiving the usual packet service in order to perform release processing of the signalling connection if necessary.
It is, therefore, an object of the present invention to provide a mobile communication system in which an occurrence of contention between an existing packet communication service and a new MBMS service is eliminated, a method of controlling operations of the system, and a node used in the system.
Another object of the present invention is to provide a mobile communication system in which processing complexity in the SGSN is eliminated, a method of controlling operations of the system, and a node used in the system.